Dermatologic diseases are diagnosed by the types of lesions they cause. Identify the morphology of the lesion(s) to establish a differential diagnosis (Table 6-1. Morphologic Categorization of Skin Lesions and Diseases), and obtain the elements of the history, physical examination, and appropriate laboratory and histopathologic tests to confirm the diagnosis. Specific clinical situations, such as an immunocompromised or critically ill patients, lead to different diagnostic considerations.
Table 6-1. Morphologic categorization of skin lesions and diseases.| Pigmented | Freckle, lentigo, seborrheic keratosis, nevus, blue nevus, halo nevus, melanoma |
| Scaly | Psoriasis, dermatitis (atopic, stasis, seborrheic, chronic allergic contact or irritant contact), xerosis (dry skin), lichen simplex chronicus, tinea pedis/cruris/corporis, tinea versicolor, secondary syphilis, pityriasis rosea, discoid lupus erythematosus, exfoliative dermatitis, drug eruption, actinic keratosis, Bowen disease |
| Vesicular | Herpes simplex, varicella, herpes zoster, pompholyx (vesicular dermatitis of palms and soles), vesicular tinea, autoeczematization, dermatitis herpetiformis, miliaria crystallina, scabies, photosensitivity, acute contact allergic dermatitis, drug eruption |
| Weepy or encrusted | Impetigo, acute contact allergic dermatitis, any vesicular dermatitis |
| Pustular | Acne vulgaris, acne rosacea, folliculitis, candidiasis, miliaria pustulosa, pustular psoriasis, any vesicular dermatitis, drug eruption |
| Figurate (“shaped”) erythema | Urticaria, erythema multiforme, erythema migrans, cellulitis, erysipelas, erysipeloid, arthropod bites, erythema annulare centrifigum, erythema marginatum, erythema chronicum migrans |
| Bullous | Impetigo, blistering dactylitis, pemphigus, pemphigoid, porphyria cutanea tarda, drug eruptions, erythema multiforme, toxic epidermal necrolysis |
| Papular | Hyperkeratotic: warts, corns, seborrheic keratoses Purple-violet:lichen planus, drug eruptions, Kaposi sarcoma, lymphoma cutis, Sweet syndrome Flesh-colored, umbilicated: molluscum contagiosum Pearly: basal cell carcinoma, intradermal nevi Small, red, inflammatory: acne, rosacea, miliaria rubra, candidiasis, scabies, folliculitis |
| Pruritus1 | Xerosis, scabies, pediculosis, lichen planus, lichen simplex chronicus, bites, systemic causes, anogenital pruritus |
| Nodular, cystic | Erythema nodosum, furuncle, cystic acne, follicular (epidermal) inclusion cyst, metastatic tumor to skin |
| Photodermatitis | Drug eruption, polymorphic light eruption, lupus erythematosus |
| Morbilliform | Drug eruption, viral infection, secondary syphilis |
| Erosive | Any vesicular dermatitis, impetigo, aphthae, lichen planus, erythema multiforme, intertrigo |
| Ulcerated | Decubiti, herpes simplex, skin cancers, parasitic infections, syphilis (chancre), chancroid, vasculitis, stasis, arterial disease, pyoderma gangrenosum |